Method and formulations for producing diffuse infrared reflection coating

ABSTRACT

An electroplated chromium finish and a method for applying chromium which produces a stable diffuse grey surface having high infrared reflectance.

United States Patent 1191 I 1 11); in w 1111 3,8162% Greenberg 1 June 111, 1974 [54] METHOD AND FORMULATIONS FOR 3,442.777 5/1969 Woods ct a1 204/51 PRODUCING DIFFUSE INFRARED 3,445,256 5/1969 Dalton 350/1 X 3,454,474 7/1969 Woods et a1 1 204/51 REFLECTION COATING 3.766.023 11/1973 Hart 204/51 X [75] Inventor: Melvin Greenberg, Annapolis, Md. 1 [73] Assignee: The United States of America as OTHER PUBLICATIONS represented the Secretary of the Morisset et a1. Chromium Plating, R. Draper Ltd, Navy, Washmgton, D.C. England, 1954 pp 27 32 [22] Filed: Oct. 25, 1968 [21] Appl. No.: 772,063 Primary ExaminerCarl D. Quarforth Assistant ExaminerR. E. Schafer [52 us. 01 204/51, 117/35 s, 117/130 R, E'Hodges 350/1, 356/51 [51] Int. Cl C23b 5/06 [58] Field of Search 204/51, 41; 350/1; 356/51; [57] ABSTRACT 343/18 A; 117/35 130 R An electroplated chromium finish and a method for applying chromium which produces a stable diffuse [56] References cued grey surface having high infrared reflectance.

UNITED STATES PATENTS 3,400,156 9/1968 Milionis et a1. 350/] X 3 Claims, 3 Drawing Figures PATENTEBJUNI 1 I974 CURRENT DENSITY (Amps./ sq.in.)

/= REFLECTANCE 3.816.271 SHEET 10F 2 20 22 24 2e 28 3o 32 H2 s0 CONCENTRATION m (L84 -q V GRAY CHROMIUM 80 so so GRAY ENAMEL WAVELENGTH microns INVENTOR F /6 2 MEL w/v GREENBERG AGENT ATTORNEY PAIENTEDJuM I am SPECTRAL REFLECTANCE 3.816271 SHEET 2 OF 2 GRAY CHROMIUM GRAY ENAMEL 0 IO 20 3O 4O 5O 6O 7O 8O 90 I00 DEGREES FROM NORMAL FIG. 3.

INVENTOR MEL Vl/V GREE/VBE AGE/VT METHOD AND FORMULATIONS FOR PRODUCING DIFFUSE INFRARED REFLECTION COATING I The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention relates to a chromium coating and in particular to a coating having visual camouflage properties and in addition, a low emittance of light in the infrared range.

The previous camouflage coating for use on naval vessels has been a grey paint having a dull or matte finish to inhibit visual discovery of the vessel.

While this paint is effective for this purpose it exhibits a high emittance or low reflectance of light of wavelength in the infrared range.

In modern warfare infrared detection techniques have become highly developed and the development of infrared counter-measures has become necessary. Since infrared emission increases with surface temperature, one technique employed to reduce such emission has been to artifically cool exposed surfaces of the vessel or provide thermal insulation around the heat source. These techniques are effective to reduce infrared emission but are relatively expensive. and add pararequired for a given piece of-equipment.

This invention provides achromium plating for metal surfaces which provides a dull, diffuse surface in a color suitable for visual camouflage purposes and exhibitsa greatly reduced emission of infrared light.

SUMMARY OF THE INVENTION The invention described herein provides .a stable chromium plating for metal surfaces and a method for applying the plating, which produces a surface finish having a dull diffuse grey color and the high corrosion and oxidation resistance of chromium and which exhibits a low emission of light in the infrared wavelength range.

The plating is applied using a plating bath having a high acid content which is maintainedat a temperature between 40C and 55C and is applied to a surface by an electroplating method using relatively high current densities.

The surface produced by this method has a dull grey appearance similar to standard matte grey ship paints yet emits only approximately percent of the infrared light emitted by the painted surface under the same conditions.

It is therefore an object of this invention to provide a plated finish suitable for use on exterior surfaces of naval vessels.

It is a further object of this invention to provide a plated finish having a dull diffuse surface and a low infrared emission.

It is another object of this invention to provide a plated chromium finish having a dull grey appearance and a low infrared emission characteristic.

It is yet another object of this invention to provide a method for applying a diffusechromium plating to a metal surface.

3O sitic weight to the vessel as well as increasing the space a .with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a chart of plating current density vs. acid concentration for a specified bath temperature range.

FIG. 2 is a chart of spectral reflectance vs. light wavelength for the subject finish and for standard grey enamel.

FIG. 3 is a chart of spectral reflectance vs. light incidence angle for the subject finish and standard grey enamel.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 there is shown a chart on which are shown the limits for plating current and sulphuric acid concentration in the plating bath which will produce a chromium plated finish having a diffuse grey surface appearance and a high reflectance in the infrared wavelength range.

A typical plating bath for'achieving the desired finish according to the invention would contain 250g of CrO 11g of granular NaSiF and 21.5 ml of H 80 having a specific gravityof 1.84 in one liter of solution with the temperature of the'bath maintained at a temperature between-40C and 55C. In accordance with the limits given in FIG. 1, the current density range required to achievea satisfactory finish-with this solution would be from-4.5 amps/square inch to 5.7 amps/square inch. Thus the chart of FIG. 1 defines an envelope of the variable parameters of the plating method within which a satisfactory finish will be produced in a solution having a chromate/sulfate concentration ratio of approximately 5:1 and a bath temperature of between 40C and 55C. It will be appreciated by those skilled in the art that this chromate/sulfate ratio is substantially higher than the ratio normally used in producing an electroplated chromium surface. The surface produced is a dull grey diffuse coating having a uniform granular appearance under X magnification.

Referring now to FIG. 2 there is shown a chart in which the percent surface reflectance is charted against light wavelengths in the infrared range. One curve represents the normal infrared reflectance characteristic of a matte grey enamel such as Haze Gray 27, MIL-E- 15130C, Formulat 5H typically used as a finish for exterior surfaces of naval vessels. The other curve represents the same characteristic of a surface finish applied according to the invention; both surfaces having similar visual appearances. As shown in FIG. 2 the presently used matte grey enamel exhibits a reflectance in the 3.0 to 15.0 micron range of from 5.0% to slightly over 10.0% while the chromium plate ranges from slightly over 50 percent at 3.0 microns to over 90 percent at 15.0 microns.

FIG. 3 is a chart representing reflectance at a 10 micron wavelength at angles from normal up to from normal for the standard naval matte grey enamel and a chromium plating applied according to the invention.

Again the advantage of the diffuse grey chromium finish over the presently used finish is obvious.

The significantly higher reflectance of the chromium finish in the infrared range makes it an ideal surface for areas of otherwise high infrared emission in order for the vessel to avoid detection by infrared sensors from normal and angular directions while at the same time providing a diffuse dull grey finish suitable as visible camouflage.

A surface having low infrared emittance has of course, other uses than those described above. For example. in the field of optical measuring equipment, a diffuse coating having high infrared reflectance would be ideal for an integrating sphere for light in the infrared range.

It is to be understood that the invention is not limited to the exact details shown and described, for obvious modifications will occur to those skilled in the art.

What is claimed is:

1. An electroplating bath for producing a diffuse chromium plating comprising an aqueous solution of 21.5 to 30 ml H 50 per liter of solution and CrO in amounts to provide a ratio of about five parts CrO to one part H 50 by weight.

2. A method for electroplating chromium to produce electro deposits having a diffuse grey surface comprising the steps of:

preparing an aqueous electroplating bath comprising essentially 21.5 to 30 ml H 80 per liter of solution and CrO in a ratio to provide about five parts CrO to one part H 80 heating said bath to a temperature in the range of about 40C to 55C; and

applying electroplating current at current densities in proportion to H 50 concentration according to FIG. 1.

3. An article comprising a structure having therein a diffuse grey chromium coating comprising spectral reflectance of from 50 percent to 90 percent of infrared the method of claim 2. 

2. A method for electroplating chromium to produce electro deposits having a diffuse grey surface comprising the steps of: preparing an aqueous electroplating bath comprising essentially 21.5 to 30 ml H2SO4 per liter of solution and CrO3 in a ratio to provide about five parts CrO3 to one part H2SO4; heating said bath to a temperature in the range of about 40*C to 55*C; and applying electroplating current at current densities in proportion to H2SO4 concentration according to FIG.
 1. 3. An article comprising a structure having therein a diffuse grey chromium coating comprising spectral reflectance of from 50 percent to 90 percent of infrared light in the range of 3-15 microns wavelength, said coating being produced by electroplating according to the method of claim
 2. 